The present invention relates to a display apparatus having a display panel in which display pixels are arranged in matrix and a driving device for displaying adapted to deliver the display panel gray scale voltages matching with display data and more particularly to, a display apparatus using liquid crystal, organic EL, plasma or the like and a driving device for displaying adapted for use in the same.
JP-A-6-348235 discloses a liquid crystal panel having X-signal lines and Y-signal lines, a horizontal driver for selecting, on the basis of a data signal of an image to be displayed, one gray scale signal from a plurality of gray scale signals deliver out of a gray scale voltage generating circuit and delivering the selected gray scale voltage to an X-signal line of the liquid crystal panel, and a vertical driver for delivering a scanning signal of the liquid crystal panel to a Y-signal line of the liquid crystal panel. It further discloses that the gray scale voltage generating circuit has a plurality of fixed resistors connected in series between a high-potential reference voltage and a low-potential reference voltage and voltage variable means for varying voltages at connection nodes of the fixed resistors between the high-potential and low-potential reference voltages. It further discloses that voltages at connection nodes of the fixed resistors are delivered as gray scale signals. It further discloses that the voltage variable means includes a variable resistor connected between the high-potential and low-potential reference voltages and an operational amplifier having its one input terminal connected to a voltage variable terminal of the variable resistor and its output terminal connected to a predetermined connection node of the plurality of fixed resistors.
JP-A-10-142582 discloses that a resistor ladder circuit comprised of resistors R0, R1, . . . , Rn and a resistor ladder circuit comprised of resistors R0′, R1′, . . . , Rn′ are connected between a power supply terminal Vcc and a connection terminal GND, operational amplifiers OP1, OP2, . . . , OPn are connected between the two resistor ladder circuits, and a constant voltage generating circuit comprised of an operational amplifier OP0 is connected to a node of the resistors Rn−1′ and Rn′. It further discloses that output currents of the operational amplifiers OPn and OP1 are adjusted by the resistors Rn and R1 and an output current of the operational amplifier OP0 is adjusted by the resistor Rn′.
JP-A-2001-22325 discloses a liquid crystal display apparatus having a voltage division circuit for generating a plurality of positive-negative symmetrical reference voltages from positive and negative reference voltages, a variable voltage generating circuit for supplying positive-negative symmetrical reference voltages for gray scale adjustment to one pair of positive-negative symmetrical voltage division points corresponding to a specified halftone of the voltage division circuit, and one pair of amplifiers. It further discloses a liquid crystal display apparatus having a voltage division circuit for generating a plurality of positive-negative symmetrical reference voltages from positive and negative reference voltages, a plurality of variable voltage generating circuit for supplying positive-negative symmetrical reference voltages for gray scale adjustment to a plurality of pairs of positive-negative symmetrical voltage division points corresponding to a plurality of specified halftones of the voltage division circuit, and a plurality of differential amplifiers.
But none of the above prior arts take the following problems into account.
Firstly, at the output of the gray scale voltage generating circuit, capacitive components including liquid crystal are charged/discharged simultaneously at a timing of A.C. (Alternating Current) operation. For the purpose of compensating the phase for an abrupt current change due to the charge/discharge, it is general to connect a stabilizing capacitor of 0.1 to 10 μF to the output of a voltage follower circuit. The stabilizing capacitor having a large capacitance as above needs to be provided externally of an IC even when the gray scale voltage generating circuit is implemented in an IC form, thus increasing the number of parts. Secondly, in the liquid crystal display apparatus, with the aim of preventing an image quality degradation similar to print, there needs a so-called A.C. operation for inverting, at a constant period, the polarity of a voltage applied to liquid crystal. In this phase, through a so-called asymmetric drive method for instance that makes individual levels of gradation voltages different at the positive and negative polarities, the amplitude of common voltage can be reduced and an image quality degradation such as flicker can be prevented to advantage. To realize the asymmetric drive with the gray scale voltage generating circuit, the level of reference voltage may be different for the positive and negative polarities. But, with the level of reference voltage changed periodically, the stabilizing capacitor is charged/discharged and as a result, consumption power increases.
Thirdly, in the liquid crystal display apparatus, an instance is supposed in which the number of colors possessed by input display data is smaller than the number of levels of generated gray scale voltages. In that case, unneeded gray scale voltages are generated by means of a ladder resistor, with the result that a consumptive steady current flows through the ladder resistor.